1. Field of the Invention
The present invention relates to a piezoelectric ceramic constituted by polycrystal of tungsten bronze structure, as well as a manufacturing method thereof.
2. Description of the Related Art
Piezoelectric ceramics are used as piezoelectric elements. Piezoelectric elements are used as sensor elements and electricity generating elements, among others, by applying the piezoelectric effect of converting mechanical energy to electrical energy. Piezoelectric elements are also used as vibrators, sound generators, actuators, supersonic motors, etc., that apply the reverse-piezoelectric effect of converting electrical energy to mechanical energy. In addition, piezoelectric elements are used as circuit elements, vibration control elements, etc., by combining the piezoelectric effect and reverse-piezoelectric effect.
PZT material expressed by the composition formula Pb(Zr,Ti)O3-PbTiO3 and PLZT material expressed by the composition formula (Pb,La)(Zr,Ti)O3-PbTiO3 are widely known as high-performance piezoelectric ceramics. However, these piezoelectric ceramics contain Pb which is harmful to the human body.
Among the Pb-free piezoelectric ceramics, or piezoelectric ceramics not containing Pb, those of tungsten bronze structure are known as having relatively favorable performance (refer to Reference Literatures 1 to 6). Patent Literatures 1 to 5 study Pb-free piezoelectric ceramic compositions, while Patent Literature 6 studies crystal orientation of a Pb-free piezoelectric ceramic.